[Elecraft] KPA100 Issue

[Don Wilhelm]

Dave,

It is correct that the re-tightening be done after the initial assembly
(after 10 to 20 hours of transmit operation).  It should also be done after
the thermal pads are changed.

It should only have to be done once.  It takes both time and temperature for
the pads to conform to all the irregularities of the heat sink and the
transistors, but once that happens it should be good for the life of the
pads.

For those who had not remembered - yes, do it, the life of your PA
transistors depends on it.

73,
Don W3FPR

> -----Original Message-----
>
> Though there is some mention about tightening the screws that
> mount the final power transistors in the manual, it can be easily missed.
>
> When I first built the KPA100 I made sure the transistor hear
> sink mounting screws were tight.  After operating the rig for
> about a week (and heat cycling the heat sink) I had an
> opportunity to open up the K2 to show a friend. At that time
> something in my mind reminded me to recheck the final transistor
> heat sink mounting screws (please remember the screws were
> carefully tightened upon assembly) and to my surprise I could
> easily tighten the screws 1/2 turn or more! It seems the heat
> conducting material cold flows a bit between the final
> transistors and the heat sink.
> So for those who have a KPA100 it would be prudent to check those
> final transistor heat sink mounting screws every so often. If you
> don't you could lose your finals.
>
> 73
>
> Dave KD1NA
>
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